Refractory tube



Patented June 2, 1953 UNITED ASTATI-:s PATENT oFFlcE RIEFRACTORY TUBE Lowell H. Milligan, Worcester, and Osgood J. Whittemore, Jr., Princeton, Mass., assignors to Norton Company, Worcester, Mass., a corporation of Massachusetts Application November 21, 1950, Serial No. 196,796

4 Claims. l

The invention relates to refractory tubes.

One object of the invention is to provide a highly refractory tube having high thermal shock resistance. tion is to provide a refractory tube having high thermal conductivity. Another object of the invention is to provide a refractory tube having one or more of the above characteristics which is resistant to molten steel.

Another object of the invention is to provide a refractory tube of two concentric portions, in which the two concentric portions have different characteristics adapted for practical` use such as beneficiating steel by additions thereto and in 4which the two portions have similar coefficients of thermal expansion. Y l

Other objects will be in part obvious or in part pointed out hereinafter. y n

In the accompanying drawings illustrating our invention: Y

Figure 1 is an axial sectional view of a composite tube in accordance with the invention wherein the silicon carbide portion is on the inside,

Figure 2 is an axial sectional view of a tube according to the invention wherein the silicon carbide portion is on the outside,

Figure 3 is an end elevation of the tube of Figure 1,

Figure. is an end elevation of the tube of Figure 2.

For applications where a tube is to be inserted into molten steel for introducing material such as deoxidizers like boron addition agents, or silicon carbide, or purifiers such as calcium carbide thereinto, we provide a composite tube such as shown in Figures 1 and 3 wherein the outer portion Ill is mullite or Zircon, and the inner portion I I is ceramic bonded silicon carbide. Silicon carbide compositions have high thermal shock resistance and high thermal conductivity but will dissolve in molten steel. Mullite and Zircon have better resistance toward molten steel but do not have such high thermal shock resistance nor such high thermal conductivity. To obtain the advantages of the several materials the silicate selected from the group consisting of mullite and Zircon is placed on the outside where it will contact the molten steel Whereas the ceramic bonded silicon carbide is on the inside where it is protected from the molten steel. Thereby deoxidizers or purifiers can be introduced into the steel near the bottom of the melt where they will do the most good. Various additions are made to steel in the ladle. If the ad- Another object of the inven A ditions are simply dropped into the ladle since cost of them are lighter than steel, they float on top and become part of the slag and have practically no effect so far as beneciating the steel is concerned. It is desirable to introduce the addition agents near the bottom of the ladle or near the bottom of the molten steel wherever it is to be beneciated (as perhaps in the open hearth) whereby the benelilciating agent will dissolve in the steel before it has time to rise to the top. Consequently a refractory tube such as shown in Figures 1 and 3 is useful for this purpose for the tube can be pushed well downv intol the bath of molten steel, in the ladle or otherwise, connected to gas pressure enough to prevent the steel from rising thereinto, and then the addition agent or agents can be run down the tube into vthe steel,.

the vgas pressure being great enough to cause a slight 'bubbling and thus to carry the addition steel is allowed to run throughthe tube. Referring now to Figures 2 and 4, the tube has an outside v.portion I2 of ceramic bonded silicon carbide and an inside portion I3 of silicateselected from` the group consisting of mullite and Zircon. Here the silicate resists the attack by the steel, that is to say it will not dissolve therein while the silicon carbide provides desirable thermal shock resistance and thermal conductivity. rIhere are many applications whereit is desired to take `molten steel from one point to another pointbywallowing it to flow.

The ceramic Ibonded silicon carbide may be made in accordance with U. S. Letters Patent No. 2,118,789 of May 24, 1938, to Henry C. Fisher or it can be made as described in U. S. Letters Patent No. 2,515,416 of July 18, 1950, to Lowell H. Milligan. Many other formulae Ifor the ceramic bond are known and may be used. The ultimate bond in many cases includes ceramic bonding constituents derived from impurities in the silicon carbide grain or by reactions with the silicon carbide of the kiln atmosphere during ring. The silicon carbide portion should be at least 50% silicon carbide by weight. We prefer that the portions II and I2 be relatively dense, that is having no fmore than 261% pores by volume.

The material from Vwhich the portions l0 and I3 are manufactured is preferably a mixture of particle sizes of Zircon or mullite, as the case may be, with ceramic binder. The above particle size mixture which is mostly in the size range coarser than 325 mesh should constitute at least 50% by weight of portions I0 and I3. The ceramic binder may be developed from such materials as clays, bentonite, etc. If bentonite is used as little as 1% or 2% may give a strong product, but useful articles can be made having as much as 20% ceramic material such as clay or a mixture of clays with or without the addition of one or more fluxes or llersf; We may' usea. small amount of temporary binder. such as dex-l trine, to give the articles green strength, and of course this burns out during the firing.

The manufacturing procedure may be. to, fill,

a rubber lined hydraulic mold having a ste'ecore rod with one mixture, apply". the-'hydraulic presB17 sure to compress this mixture; release. the' hy."-

draulic pressure which will CauSetIIeIIi-bber'liner to expand again, ll the remaining space With the second mixture, apply the pressure. a-.second time, remove the pressed composite tube from the mold, dry it, then fire it at cone IB. Hydraulic molding with iiexible rubber liners is now Well knownso it need not further bezdescribed here@ The silicon carbide is of courseV a product` of. the'.- electricy furnace and any. commercial grade of. silicon carbide can be used. Commercial. grades-y vary from 951%; to better than 99%. pure; Naturallythe. purer.l varieties; are preferable but are also a littlefmorev expensive and thei'lessnpure grades-.willgivesatisfactory results irr thisfinvention.

lvlullite is` acompound ofi the formula 3AliO3.2SiO2z Althoughitrarely occurs-in natureit 'caribe synthesized'in thefelectrc'furn'ace. In' practical mullitematerials there may be excess; aluminawhich may'existas' alpha; alumina oir exces'si silica; which. may" exist-1 as silice'ous: glass;y Mullite may alsoy be: developed by calcining alumino silicate* minerals in which case X-rays may shov.r that' more mullitel exists than is `indicated by' microscopic examinations;

Zircon]- is zirconium silicate Z'rSiOif..y Itis found in nature/and can be fused andV purified inthe electric furnace.

One desirable characteristicof` our composite-z tube is that each of mullite and Zircon' have c'o`- efficients of thermal expansionv close toV that of ceramic bonded silicon carbide; Consequently" tubes: made in accordance With-thisinvention will not crack during use as indicated above norwill? thel outerportion separate deleteriou'sly from theinner portion when the composite tube isI heated andcooled.

It will thus be seen that there has been provided by this invention a refractory tube in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many clziange'smight be? made lntheembodiment above set; forth, it is t'o-be understood that all matter hereinbefore described or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

We claim:

1.. Are'factorytube consisting of at least two portions# concentdally related and integrally ineki'`- one"` oi'saidff-portions being inner of the otherofsaid portions, one of said portions being of` ceramic bondedfsilicon carbide, said ceramic bonded silicon carbide portion being at least 563%l byfweight silicon carbide, said other portion being at least 50 by Weight silicate, said silicate being." selected from. the: groupy consisting of mulliteland Zircon.

2. Av refractory tube consisting of at leasttwfoportions concer'itricaillyV related and integrallyf joined', oneof said portions being inner of the* other `of sadf portions?, one of`r sai'dfportions'v being off ceramicA bonded silicon carbide; said ceramic bonded sil-iconc'arlciid'e'l portion-being" at least 50% by weight silicon carbide'V and having' not' more than-26`% pores, said'othe'r por-'tion being atleast 56%', by Weightl silicate, said silicate being selected from the' group' consisting 'of mullite and' Zircon.

3". A refractory tube` accordingto claim- 1 in which the sil-iconcarbide'- portion` is inside of the silicate portion.

4. A' refractory tubel according t'o claim 1 in which the silicon carbide portion isoutsid'eof :the-

silicate portion.-

Lovvnu. H. MfmGAN. g OSG-GB" J'. JR.

References Cited in the le of this patenty UNITED STTES P'IENTS` Number lSl'arrieL4 Date'.

1,949,731; someten Mar: e; i934" 2,308,307 HOblST Jan'. I2', 1943 2,408,467 Lyons 1 Oct. 1, 1946' 2,447,672 Sm'th'l l.' Allg. 245,Y 1948. 

1. A REFRACTORY TUBE CONSISTING OF AT LEAST TWO PORTONS CONCENTRICALLY RELATED AND INTEGRALLY JOINED, ONE OF SAID PORTIONS BEING INNER OF THE OTHER OF SAID PORTIONS, ONE OF SAID PORTIONS BEING OF CERAMIC BONDED SILICON CARBIDE, SAID CERAMIC BONDED SILICON CARBIDE PORTION BEING AT LEAST 50% BY WEIGHT SILICON CARBIDE, SAID OTHER PORTION BEING AT LEAST 50% BY WEIGHT SILICATE, SAID SILICATE BEING SELECTED FROM THE GROUP CONSISTING OF MULLITE AND ZIRCON. 